The issue is, once they cap, they go down but not up. Once you hit the cap you can't gain approval anymore, just lose it. It may actually lock in, the values are hidden so I can't be sure, but what I am sure of is, there's a point where you can only lose approval. It's usually too far into the game to matter, but with DLC, and possible approval/disapproval options, it could end up being an issue.
For example, once Solas' approval is capped, he won't gain anymore approval when activating artifacts, or asking questions. He will however still lose approval if he disagrees. Even after that approval goes down, activating artifacts, or asking questions will still not raise it. In the main game that's not big deal, to max it out you're likely near the end, but with 4 DLCs, there could be a point where it just keeps dropping, with no way to bring it back up, and you're stuck with a guy that hates you. Now, if that can affect romances, that could end up being an even bigger issue for some who can't even lock those in due to approval only dropping.
For the record, I really liked DA2's implementation, because it was based primarily on choices, swung both ways, and was worked into their personal skill trees (all elements I enjoyed).